1. Field
Embodiments of the present invention relate to a brake master cylinder configured to sense variation in magnetic flux in accordance with operation of a piston installed with a magnet, and thus to control activation of brake lamps.
2. Description of the Related Art
Generally, a master cylinder for a brake of a vehicle receives force boosted in a booster using a pressure difference between vacuum and atmosphere, converts the received force into hydraulic pressure, and then transfers the hydraulic pressure to a wheel cylinder, to generate braking force.
Such a brake master cylinder is provided with a means to sense operation of a piston in order to turn on a lamp in accordance with the sensed result. FIG. 1 schematically shows a conventional brake master cylinder, which may control activation of brake lamps.
Referring to FIG. 1, the master cylinder 10 includes a piston 12 to be slidably moved in the master cylinder 10 by pedal pressure from a pedal (not shown). The piston 12 is formed with a groove 12a, in which a magnet 20 is mounted. A Hall sensor 30 is installed on an outside of a cylinder body 11 included in the master cylinder 10 at a position corresponding to the magnet 20.
The Hall sensor 30 includes a case 31 fixed to the outside of the cylinder body 11, a magnetic detector 33 attached to a base plate 32 disposed in the case 31, a control circuit 34 mounted to the base plate 32, to control the magnetic detector 33, and a lead wire 35 connected to the control circuit 34. The magnetic detector 33 includes a magnetoresistive element a Hall element, or a lead switch, which exhibits variation in resistance in accordance with variation in the intensity of a magnetic field sensed during movement of the piston 12. The Hall sensor 30, which has the above-mentioned configuration, turns on or off brake lamps through detection of the intensity of magnetic force corresponding to a moved position of the magnet 20 installed at the piston 12. This technology is well known in the technical field to which the technology pertains and, as such, no detailed description thereof will be given.
Meanwhile, due to the above-mentioned arrangement of the Hall sensor 30, the magnet 20 installed at the piston 12 should be disposed at a position where the magnet 20 faces the magnetic detector 33 in order to enable the Hall sensor 30, namely, the magnetic detector 33, to easily detect intensity of magnetic force.
In the above-mentioned conventional case, however, there is a problem in that the magnet 20 may be circumferentially spaced away from the magnetic detector 33 due to rotation of the piston 12 occurring during operation of the piston 12, so that the Hall sensor 30 may not reliably detect intensity of magnetic force. To solve this problem, there has been an attempt to install a ring-shaped magnet (not shown) at the piston 12. In this case, however, it may be impossible to assemble the ring-shaped solid magnet in a groove circumferentially formed at the piston 12.
In addition, installation of the ring-shaped magnet at the piston 12 may be possible when a flexible rubber magnet is used. However, such a rubber magnet is not practically employed because the magnetic force thereof is too weak to be detected by the Hall sensor 30.